1. Field of the Invention
The present invention relates to the field of hydraulic intake and exhaust valve actuation methods and apparatus for internal combustion engines.
2. Prior Art
At the present time, piston-type internal combustion engines of interest to the present invention are widely used in automobiles, trucks, buses and various other mobile and stationary power systems. Such engines include the common gasoline and diesel engines, as well as similar engines operating from alternative fuels such as liquid natural gas. These engines commonly utilize intake and exhaust valves that are spring loaded to the closed position and which are directly or indirectly opened at appropriate times by a camshaft mechanically driven from the engine crankshaft.
Camshaft actuation of engine valves historically has had a number of advantages, resulting in its relatively universal use in such engines for many decades. These advantages include high reliability, particularly given the current level of development of such cam actuated valve systems. Cam actuation is also relatively cost effective, again given the state of development and quantities in which it is produced.
However, engine valve systems are facing more and more challenges of increasing concern. In particular, optimal valve timing and lift are not fixed throughout the engine operating range. For instance, optimal valve timing and lift for maximum power at one engine speed will not be the same as optimal valve timing and lift for maximum power at another engine speed. Accordingly, the classic cam operated valve systems utilize a compromised valve timing and lift, providing compromised performance over a certain range of engine operating conditions while being less than optimal for most, if not at all, these conditions. Further, valve timing and lift for maximum power at any engine speed may not be optimal from an engine emissions standpoint. Optimum valve timing and lift at any given engine speed may need to be dependent on other dynamic engine parameters, such as one or more of engine loading, air temperature, air pressure, engine temperature, etc.
Recently, various hydraulic systems for engine intake and exhaust valve actuation have been proposed. These systems offer the potential of more flexible control of valve actuation parameters over the range of the various engine and environmental operating parameters, as their control, such as electronic control, is not subject to the constraints normally imposed by mechanical valve actuation systems. However, care should be taken to minimize the power consumption in hydraulic intake and exhaust valve actuation systems to achieve the potential advantages of such systems while minimizing power losses in the valve actuation systems.
The present invention is an improvement on hydraulic systems for engine intake and exhaust valve actuation.